#lang racket

#|

Max Sherman
CSE 341
Section 1

Things to do:
1. Introductions (Data structure, programming language, function or method, color, number)
2. Example functions
3. Practice writing racket
4. Demo

Notes about map:

2 arguments and returns a new list:
map f lst -> (new list)

Example call:
(map (lambda (x) (+ x 1)) '(1 2 3 4))  ---->  '(2 3 4 5)

Alternatively we can use the function add1 to do the same thing:
(map add1 '(1 2 3 4))  ---->  '(2 3 4 5)

|#

(define (map f lst)
  (if (null? lst)
    null
    (cons (f (car lst)) (map f (cdr lst)))))

;; "Tail recursive map".  This reverses the list so it isn't really map.
(define (map-tr f lst)
  (letrec ([map* (lambda (f lst acc)
                   (if (null? lst)
                     acc
                     (map* f (cdr lst) (cons (f (car lst)) acc))))])
    (map* f lst null)))

(define (reverse lst)
  (letrec ([reverse* (lambda (lst acc)
                       (if (null? lst)
                         acc
                         (reverse* (cdr lst) (cons (car lst) acc))))])
    (reverse* lst null)))

(define (sum lst)
  (letrec ([sum* (lambda (lst acc)
                   (if (null? lst)
                     acc
                     (sum* (cdr lst) (+ (car lst) acc))))])
    (sum* lst 0)))